Warren Buffett holds an estimated $56.5 billion worth of Berkshire Hathaway stock — the most valuable stock holdings of any active chief executive officer. Oracle CEO Larry Ellison and Amazon.com CEO Jeff Bezos have the next most valuable company stock holdings.

As many as 27 CEOs hold at least $1 billion worth of their companies’ stock, according to the most recent stock prices and ownership information. To determine the 15 CEOs with the most valuable stock ownership by market value, 24/7 Wall St. reviewed company proxy statements and recent share prices for companies with a market cap greater than $5 billion. These are the CEOs whose companies made them rich.

Click here to see the 15 CEOs

Many of the nation’s wealthiest CEOs founded the companies they run. Both Harold Hamm and Ralph Lauren began to build their current businesses in 1967, with Hamm starting out searching for oil and Lauren selling ties. In all, 12 of the 15 wealthiest CEOs are also their company’s founders. Some of these executives made all, or effectively all, of their money after founding their companies. Michael Dell and Mark Zuckerberg famously founded their businesses while in college.

Only a few of these executives made their money before their current position. Elon Musk, the current CEO of Tesla, made his first fortune from the sale of PayPal. Sheldon Adelson, founder of resort and casino giant Las Vegas Sands, first owned a successful computer trade show, called COMDEX. Adelson sold COMDEX after founding Las Vegas Sands for $800 million.

Several of these executives continue to be actively involved in multiple companies. Rupert Murdoch recently split his longtime business into two companies, Twenty-First Century Fox and News Corporation. While he is only the CEO of the former, he remains the chairman of both.

Among the three wealthiest CEOs who are not the founders, two are closely connected to the company’s founder or founding group. Steve Ballmer joined Microsoft early in its history as its first business manager and received 8% of the company’s stock on the day it incorporated. John Hess, while not the founder of the Hess Corporation, is the son of founder Leon Hess and has been the CEO of the company for more than 28 years. However, Hess was removed as the company’s chairman in favor of an independent, non-executive chairman.

Many companies with extremely wealthy CEOs are in the technology sector. This includes individuals such as Ballmer, Michael Dell and Larry Ellison of Oracle, who played major roles in developing and marketing much of the technology used today. Later, Jeff Bezos, Larry Page and Mark Zuckerberg founded companies that provide online services to hundreds of millions, or even billions, of people worldwide.

Another well-represented industry among the wealthy CEOs is the energy industry, which includes three of the nation’s wealthiest CEOs. Among these are Harold Hamm, whose company, Continental Resources, is one of the nation’s leading energy exploration and production companies. Kinder-Morgan, led by CEO Richard Kinder, has focused mostly on developing pipelines and oil terminals.

To determine the 15 CEOs with the most valuable company holdings, 24/7 Wall St. reviewed figures produced by Capital IQ. Each CEO’s total number of shares beneficially owned are based on the most recently available proxy statement. Additionally, prices used in determining total market value of their holdings are accurate as of September 8. Because stock prices fluctuate, and executives may buy or sell shares in their companies, these numbers likely will have changed slightly.

These are the CEOs whose companies made them rich.

1. Warren Buffett
> Company: Berkshire Hathaway Inc.
> Value of shares: $56.5 billion
> CEO since: 1970

Warren Buffett has been the CEO of Berkshire Hathaway Inc. (NYSE: BRK-A) for more than 40 years and has been the controlling shareholder of the company since 1965. In 2010, Buffett told CNBC that he began acquiring shares in Berkshire Hathaway in 1962, when the company was a failing textile maker. He only decided to buy up the company after feeling he had been ripped off by its former management when he offered to sell back his stock to the company. Today, less than 50 years later, Berkshire is one of the world’s largest companies, and Buffett is possibly the most celebrated investor of all time.

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2. Larry Ellison
> Company: Oracle Corp.
> Value of shares: $35.8 billion
> CEO since: 1977

Oracle Corp. (NYSE: ORCL) was founded in 1977, when three engineers formed Software Development Laboratories to build a CIA database program code-named “Oracle.” More than 35 years later, the company continues to build and sell databases, as well as a range of IT services and products, software and hardware. One of the three original founding engineers, Larry Ellison, has served as CEO from the outset. During that time, he has amassed a massive fortune, with nearly $36 billion in company stock. Outside of his role at Oracle, Ellison recently has generated controversy for his role in attempting to transform the America’s Cup, a long-running and prestigious sailboat race, into a made-for-TV event. Critics have accused Ellison of allowing participation in the event to become too dangerous after a New Zealand team sailor died in practice.

3. Jeff Bezos
> Company: Amazon.com Inc.
> Value of shares: $25.4 billion
> CEO since: 1996

Jeff Bezos founded Amazon.com Inc. (NASDAQ: AMZN) in 1994. By July 1995, the company began selling products online. Less than two years later, in May 1997, the company completed an initial public offering (IPO) at just $18 a share (or, splits adjusted, just $1.50 a share, according to the company). Currently, shares trade at close to $300. In 1999, Time magazine named Bezos Man of the Year, and he was hailed as having changed retail. Recently, Bezos has been in the news for his purchase of the Washington Post for $250 million in cash from the Washington Post Co.

4. Sheldon Adelson
> Company: Las Vegas Sands Corp.
> Value of shares: $24.9 billion
> CEO since: 1988

Sheldon Adelson is the founder, and current chairman and CEO, of hotel and casino company Las Vegas Sands Corp. (NYSE: LVS). According to the company, Adelson first found success as a trade show owner — he started the computer trade show COMDEX in 1979 and later sold it for $800 million in 1995. Adelson bought his first hotel, the Sands Hotel, in 1989 and began building his resort empire in 1996, when he imploded the Sands Hotel to build The Venetian. Adelson was key in helping to bring convention travelers to Las Vegas, the company notes, and his relatively early expansion into Asia was hailed as highly successful. In addition to his work with Las Vegas Sands, Adelson is also a prominent political donor and supporter of the Birthright Israel Foundation.

5. Larry Page
> Company: Google Inc.
> Value of shares: $21.5 billion
> CEO since: 2011

Larry Page is the co-founder of search engine giant Google Inc. (NASDAQ: GOOG), along with Sergey Brin. The two started Google in 1996 as a research project while they were Ph.D. candidates at Stanford University. Initially, the search engine was called BackRub and ran on the university’s server. By 1998, Google had incorporated and was named by PC Magazine as one of the year’s top 100 websites. PageRank, the key component of the company’s search algorithm, which assigns a level of importance for any given webpage, is named after Larry Page. In 2004, Google went public, turning more than 1,000 employees into millionaires while making Page and Brin billionaires. In 2006, Google acquired YouTube, giving the company ownership of two of the most widely trafficked websites in the world. In early 2011, Page was named CEO of Google, replacing Eric Schmidt, whom Page and Brin had hired in 2001 to help manage and direct the company.

6. Mark Zuckerberg
> Company: Facebook Inc.
> Value of shares: $18.7 billion
> CEO since: 2004

Mark Zuckerberg founded Facebook at Harvard in early 2004, along with help from classmates Chris Hughes, Dustin Moskovitz and Eduardo Saverin. By the end of the year, the site had more than a million users. From there, Facebook only continued to grow in popularity. By October 2012, according to the company, Facebook had more than a billion users. Along with the company’s growth, Zuckerberg’s wealth has grown as well — he was worth nearly $19 billion at the end of the last fiscal year. But not all news about the company has been positive. Most recently, the company’s initial public offering was deemed a monumental failure. Facebook Inc. (NASDAQ: FB) initially was valued at more than $100 billion, yet shares fell immediately after the IPO and did not regain their initial valuation until about a year later.

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7. Harold Hamm
> Company: Continental Resources Inc.
> Value of shares: $13.8 billion
> CEO since: 1967

Harold Hamm is the CEO of Continental Resources Inc. (NYSE: CLR), one of the nation’s largest oil exploration and production companies. He has served in this role since 1967 when he founded Shelley Dean Oil Co., the predecessor company to Continental. The company is a major player in the Bakken area, and it was the largest leaseholder in the region at the end of 2012. Because of his role in the oil industry, Hamm was named to the Time 100 list of the world’s most influential people in 2012. Oklahoma Senator James Inhofe honored Hamm for Time magazine: “Through the use of hydraulic fracturing and other new technologies, Hamm, 66, has created hundreds of jobs and homegrown energy.”

8. Rupert Murdoch
> Company: Twenty-First Century Fox Inc.
> Value of shares: $10.4 billion
> CEO since: 2013

The 82-year-old CEO and co-founder of Twenty-First Century Fox Inc. (NASDAQ: FOXA), Rupert Murdoch spent more than six decades building his multinational media empire. In June, the company split from News Corp, the publishing division responsible for publications such as The Wall Street Journal, in part due to losses in its print newspaper operations. The split came in the wake of the widely publicized phone-hacking and bribery scandal within the defunct British newspaper News of the World, which was controlled by News Corp.

9. Steve Ballmer
> Company: Microsoft Corp.
> Value of shares: $10.4 billion
> CEO since: 2000

Steve Ballmer was one of Microsoft’s first business managers, having joined the company in 1980. Microsoft Corp. (NASDAQ: MSFT) is the global leader in software products. Best known for its Windows operating system, the company recently has begun a transformation into a devices and services company, signaled by its recent purchase of Nokia’s handset business. Since being named CEO in 2000, Ballmer’s tenure has often been criticized. During his time as CEO, Ballmer more than tripled the headcount from 39,000 to more than 131,000, including Nokia employees, according to Reuters. Over the same time, Microsoft’s share price dropped more than 40%. Last month, Ballmer revealed his intention to retire in the next year.

10. Richard Kinder
> Company: Kinder Morgan Inc.
> Value of shares: $8.5 billion
> CEO since: 1999

Richard Kinder, who co-founded Kinder Morgan Inc. (NYSE: KMI) in 1997, has helped grow the business into the nation’s largest midstream oil company. Today, Kinder Morgan has more than 11,000 employees, as well as roughly 80,000 miles of pipelines and 180 terminals, according to its website. While Kinder is paid just $1 a year, his stake in the company is worth more than $8.5 billion. His company also serves as a general partner in several master limited partnerships — publicly traded stakes in energy infrastructure that offer investors favorable tax treatment.

11. Elon Musk
> Company: Tesla Motors Inc.
> Value of shares: $4.7 billion
> CEO since: 2008

PayPal founder Elon Musk is currently the CEO of both Tesla Motors Inc. (NASDAQ: TSLA), an electric car company, and SpaceX, a rockets and spacecraft company. Musk began running Tesla as CEO in 2008, just five years after he help found the company. Within two years, in 2010, Tesla went public and today is worth more than $20 billion. SpaceX was responsible for the first privately developed spacecraft — the SpaceX Falcon 1 — which successfully entered space and orbited around the Earth. Musk is a hands-on chief executive, who oversees and participates in design and development. He additionally served as chairman of alternative energy company SolarCity Corp.

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12. Michael Dell
> Company: Dell Inc.
> Value of shares: $3.8 billion
> CEO since: 2007

Michael Dell founded his namesake company in a college dorm room in 1984. By 1992, Dell was the youngest CEO at the time to make the Fortune 500 list. This year, Dell is poised to reacquire the PC maker for $24.9 billion. In the past several years, Dell Inc. (NASDAQ: DELL) has struggled, due in part to the rising popularity of smartphones and tablets, which has accelerated the decline of the PC market. As a private business, Dell will attempt to transition its focus towards providing software and enterprise services.

13. Ralph Lauren
> Company: Ralph Lauren Corp.
> Value of shares: $3.7 billion
> CEO since: 1967

Ralph Lauren founded what would become Ralph Lauren Corp. (NYSE: RL) in 1967, when the designer’s ties first appeared in department stores. From there, Lauren continued to develop new ideas, including using men’s fabrics for womens’ clothing and his famous polo shirt. In 1997, he took his company public. Presently, Ralph Lauren has multiple brands in addition to the well-known Polo Ralph Lauren, including luxury, athletic wear and denim-focused lines. The company also has two restaurants located in Chicago and Paris.

14. John Hess
> Company: Hess Corp.
> Value of shares: $2.3 billion
> CEO since: 1983

Leon Hess founded Hess Corp. (NYSE: HES) in 1933 as an oil delivery business near his home in New Jersey. With time, the company expanded beyond local delivery, purchasing oil tankers and building both oil terminals and refineries. By the 1960s, the company started opening gas stations and began offering its now-famous line of Hess truck toys. Leon Hess eventually was succeeded by his son, John. Recently, Elliott Management Corp., one of the company’s largest shareholders, heavily criticized John Hess and Hess Corp. for having a board of directors that was too entwined with the company’s management and the founding family. Elliott also accused Hess of poorly managing the company. In May, the dispute was settled with Hess being stripped of his role as chairman and the company overhauling its board of directors.

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15. Frederick Smith
> Company: FedEx Corp.
> Value of shares: $2.1 billion
> CEO since: 1977

Frederick Smith founded FedEx Corp. (NYSE: FDX) in 1971. He has served as either chairman, CEO or president, or some combination thereof, ever since. The company was a pioneer in combining air and ground express shipping. According to its website, in 1973, FedEx sent 14 Dassault Falcon jets to deliver packages across the nation on its first night of operations. Roughly 10 years later, FedEx became the first company in the country to surpass $1 billion in revenue without any merger and acquisition activity. Currently, FedEx has more than $44 billion in annual revenues and more than 300,000 employees. Smith’s ownership stake, totaling more than 6% of the company, is worth more than $2 billion.

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